A retravirus has been isolated from goats with chronic arthritis and demyelinating encephalitis. This is apparently a new virus, heretofore undescribed. Experiments are underway to prove that this virus causes chronic arthritis and demyelinating encephalitis. It is being characterized morphologically and biochemically. It has a reverse transcriptase, and the product of that enzyme will be used as a probe to determine whether the virus is endogenous in goats. The site of virus replication will be determined by immunofluorescence in vivo. Immunologic studies will be conducted to reveal the relationships existing between the immune response and the development of subsequent disease. We will use molecular hybridization and radioimmunoassay to define the relationship between this virus and retravirus of closely related animals.